You may get .psd* file of with watermarked original stock images layers(!) of the "Christmas Night. Magic scene with flying Santa" Photoshop tutorial by making a payment. Put the tutorial title in "Add special instructions to seller" line of PayPal and it will be sent to you shortly.

Fill white layer below trees image with similar color spots like on the screen shot. Use Eyedropper tool to pick color from winter scene layer. Just keep active Brush Tool and click with it to color spots with the pressed "Alt" on your keyboard.

In order to remove trees layer contour and make background more realistic, correct your airbrush settings. Use Opacity and Flow parameters around 35%.

Fill it with black and white linear gradient just like on the screen shot.

In order to make clouds contour more realistic, process bottom part of the sky with the soft translucent brush(Brush Tool Opacity should be around 35-50%). Make these corrections in the Layer Mask, check out that the mask thumbnail is active.

You may see here the processed area.

Then you may merge all created layers.

Make the top part of the tallest tree. Select the head of the next tree using Lasso Tool.

Copy and paste selected tree head into the new layer.

Apply Custom Warp transformation to make this shape little bit different than the original.

Erase outside background with the soft Eraser Tool.

You may create funny and fairy twisted tips for the trees.

Draw the shape with small translucent brush(Opacity around 50%) using 3-5 white/gray shades from the original tree.

Insert snow image.

Erase the part of the image marked on the screen shot, you may use regular small round brush with the Hardness around 85-90%.

Merge all previous layers again("merged layers" on the screen shot) except the last one, leave snow surface image in the separate layer. Apply Match Color adjustments to this layer.

Go to Image > Adjustments > Match Color. In the Source menu choose current psd file and last merged layer from the Layer drop down menu. Play with Image Options to find better result of color corrections.